DESCRIPTION: The RuvABC system of proteins function in homologous recombination and recombinational repair. The central player in the system is the RuvB protein, which is a hexameric helicase. RuvB is targeted to Holiday junctions by RuvA. The structures of the hexameric helicases have been of great interest, since they are motor proteins that couple the hydrolysis of ATP to the generation of motion along DNA and the breaking of the DNA duplex into single stranded components. At this time, these proteins have eluded crystallographic structural analysis because of the lack of suitable crystals. This problem has now been overcome by work on the RuvB protein from the thermophilic bacterium Thermotoga martima. Crystals of the RuvB helicase from this organism have been obtained that diffract to 2.0 Angstrom resolution, and a structure determination is very likely to be successful. In addition, the RuvB helicase from E. coli and Thermus thermophilus have also been crystallized. The diffraction properties of these proteins are not yet of sufficient quality, and these crystals will be improved. The ultimate aim of the project is to obtain structural information on the RuvAB Holliday junction complex, and a combination of biochemical and crystallographic studies, as well as mutagenesis, will be directed towards that end. The work proposed here is likely to lead to fundamental advances in our understanding of helicase mechanism.